What is the UX behind the caret symbol used when a left menu is collapsed? Some applications use the left caret and some use the right. What's the ideal approach?
Toggles will always be confusing, as explained by others:
As the learning curve is small, the best thing to do is make a consistent choice that works for the visual hierachy of your UI:
- All icons represent the current state
- All icons represent the action on click
The icon used in the Patterns– Navigation drawer, Material Design Guidelines, for the action of collapsing a left menu is that left caret you mentioned.